Optical spectroscopy on individual amphi-PIC J-aggregates
Optical spectroscopy on individual amphi-PIC J-aggregates
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DOI：
10.1021/nl051132z
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发表时间：
2005-12-01
期刊：
影响因子：
10.8
通讯作者：
Köhler, J
中科院分区：
文献类型：
--
作者：
Lang, E;Sorokin, A;Köhler, J
利用低温单分子光谱技术使我们能够以前所未有的分辨率记录单个J聚集体的荧光激发光谱。的光谱出现非常不均匀，和显着的差异，相对于光谱的轮廓，光谱特征的偏振依赖性，和光化学/光物理稳定性被揭示。光谱的不均匀性与低温电子显微镜观察到的结构不均匀性是一致的。低维有机超分子结构如共轭聚合物、天然色素-蛋白质复合物或树枝状大分子近年来引起了人们的极大兴趣。1-5分子聚集体具有快速有效的能量转移、非线性光学行为和光谱性质的可调谐性等特点，使其成为开发具有定制性质的新型光电器件的有希望的候选者。在这方面，一个突出的例子是由一类被称为J-聚集体的材料代表的，J-聚集体是由数百个以各种几何形状排列的非共价结合的分子构建块组成的超分子结构。各种形式的J-聚集体已经成为许多实验和理论研究的主题6 -14，因为它们的电子激发态具有有趣的集体效应，可以观察到光学吸收的强烈红移和相对于单体的振子强度的急剧增加。事实证明，电子激发态的实际性质是由各种参数的复杂相互作用决定的，尽管付出了相当大的努力，但文献中的一个回归主题是光学激发的局部化程度。[14-17]特别提出的问题是，是否有可能观察到将激发限制在J-聚集体的相对较小部分上的迹象。13，18，19分析这些系统的激发态的巨大困难来自这样一个事实，即即使在低温下，光谱中的细节也是平均的。
Exploiting low-temperature single-molecule spectroscopic techniques allowed us to record fluorescence-excitation spectra from individual J-aggregates with unprecedented resolution. The spectra appear extremely heterogeneous, and significant differences with respect to the profile of the spectrum, the polarization dependence of the spectral features, and the photochemical/photophysical stability are revealed. The spectral heterogeneity is consistent with the structural heterogeneity observed with cryo-electron microscopy.Low-dimensional organic supramolecular structures such as conjugated polymers, natural pigment-protein complexes, or dendrimers have attracted considerable interest in recent years. 1-5 Features such as fast and efficient energy transfer, nonlinear optical behavior, and tunability of spectral properties make molecular aggregates promising candidates for the development of new optoelectronic devices with tailored properties. In this regard a prominent example is represented by a class of materials known as J-aggregates which are supramolecular structures consisting of hundreds of noncovalently bound molecular building blocks arranged in various geometries. The various forms of J-aggregates have been subject of numerous experimental and theoretical studies6-14 because their electronically excited states feature interesting collective effects which can be observed as a strong red shift of the optical absorption and a drastic increase in oscillator strength with respect to the monomers. It turns out that the actual nature of the electronically excited states is determined by a complex interplay of various parameters, and despite a considerable effort, a returning theme in the literature is the degree of localization of the optical excitation. 14-17 In particular the question is raised whether it should be possible to observe indications for a confinement of the excitation onto a relatively small segment of the J-aggregate. 13, 18, 19 The great difficulty in analyzing the excited states of these systems arises from the fact that even at low temperatures details in the optical spectra are averaged out